LHC News

Early Physics at the LHC, Sheffield May 08 1

LHC News

• End of June: The LHC is expected to be cooled down

• End of July: First particles may be injected, and the commissioning with beams and collisions will start.

• Sept/Oct: First collisions at 10 TeV.

Cooldown status 13/5/08

Early Physics at the LHC, Sheffield May 08 2

Magnet tests

• Sector 4-5 Power Tests

• Several training quenches were observed above 5 TeV equivalent currents

• Stable conditions~10 TeVHopefully!

• The magnet training for full 14 TeV operation will then be completed over the winter shutdown 2008 - 2009

Ramp of 138 power converters to a current equivalent

to 5.3 TeV (including all high current magnets realistic LHC

optics )

Early Physics at the LHC, Sheffield May 08 3

What are minimum bias events?

• Minimum bias are inelastic collisions of two protons– Includes very rare high-pt scatters and very common low-pt scatters

• Minimum bias is an experimental definition– Defined by experimental trigger and analysis

• Relation between experiment and physics is:

inelasticndinelasticndddddsdsdmeasuredfff

fi are acceptances for different physics processes determined by the trigger Trigger bias

Early Physics at the LHC, Sheffield May 08 4

Triggering Minimum bias

Two Triggers implemented:1. Random+track triggerL1 Filled bunch triggerBunch crossing rate 13.3MHz Mean no events/crossing=0.06 94:6 empty:interaction

Use L2 pixel and SCT spacepoints to reject empty events

Use tracks in EF to reject beam-gas

75ns @ L=1031cm-2s-1 mean # of interactions/crossing ~0.06

2. L1 using Minimum bias trigger scintillators

Early Physics at the LHC, Sheffield May 08 5

MBTS

• Trigger scintillation counters mounted on end of LAr calorimeter covering same radii as ID– Cover 2<||<4

• Can be used for first data BUT!– Not rad-hard– Uses 1/8th of tilecal readout Lifetime unknown

• At L1 S/N is ‘modest’ – Now in simulation can be tuned to

measurement in the summer• Can do better at L2 with precision readout

ηη=2.0=2.0

ηη=3.8=3.8interactiointeraction pointn point

Beam-pipeBeam-pipe

++ηη

pan

nel

pan

nel

MBTMBTSS

UA5

Early Physics at the LHC, Sheffield May 08 6

MBTS trigger: Trigger bias

• MBTS_1_1 requires hits in both hemispheresThis should be similar to earlier NSD triggers

• MBTS_2 requires two paddles to be hit, can be same side• Trigger bias = efficiency of trigger for specific process

Not trigger rates!

preliminary preliminary

Will Bell

Early Physics at the LHC, Sheffield May 08 7

Inner Detector Trigger at L2

preliminary

preliminary

Use pixel and SCT spacepoints to reject empty eventsEmpty:Interaction ~ 94:6Still have large beamgas contribution

L1 random trigger

Will Bell and Regina Kwee

Early Physics at the LHC, Sheffield May 08 8

Inner Detector Trigger

SCT Space Points >= 3& Pixel Space Points >=12

|η| < 2.5 & pT > 200 MeV & |Z0| < 200.0 mmTrack constraint removes beamgas through vertex constraint

preliminary

Will Bell and Regina Kwee

Early Physics at the LHC, Sheffield May 08 9

Tracking in MB events• Acceptance limited in rapidity and

pt• Rapidity coverage

– Tracking covers ||<2.5

• pT problem

– Need to extrapolate by ~x2 Need to understand low pt charge

track reconstruction

1000 events1000 events

dNdNchch/d/d

ppTT>500MeV>500MeV

ppTT~250Me~250MeVV

MC primary charged particlesMC primary charged particles

Early Physics at the LHC, Sheffield May 08 10

Low pT track reconstruction

preliminary

preliminary

Use trackspT>150MeV

M.Leyton

Track-particle correction Acceptance*efficiency*fake subtraction

preliminary

Technical details:Release 13.0.40 low pT trackingNow improved – see later

Early Physics at the LHC, Sheffield May 08 11

Minimum bias distributions

PYTHIA

Minimum bias sampleSelected by MBTS_2Corrections for:• track reconstruction• vertex reconstruction

•Multi-vertex events not looked at!

NSD sample

Distributions have pT>150MeV

6%

preliminary

preliminary

MB sample

NSD sampleCorrected for trigger bias-- change trigger bias

ATLAS has the tools to trigger on and reconstruct minimum bias events

Early Physics at the LHC, Sheffield May 08 12

Particle Composition

MB particle dominiated by low pT pions and ~10% K

• Pions– 150MeV can traverse to edge of SCT but

reduced efficiency due to inelastic collisions in ID

• Kaons– Much larger inefficiencies due to increased

inelastic collisions in ID

Efficiencies depend on relative rates of particle production in MB interactions

(Sadly CMS can do PID with analog readout)

Ian Dawson

Early Physics at the LHC, Sheffield May 08 13

0.1 < PT ≤ 0.5 (GeV)

Coming soon: Improved low pT tracking

Improved low pT turn-on

Based on two-pass tracking1. Find tracks with pT>500 MeV2. Find tracks with 100<pT<500MeV

from remaining hits, widens track finding roads

Early Physics at the LHC, Sheffield May 08 14

0.1 < PT ≤ 0.5 (GeV)

Coming Soon: Improved low pT tracking

Early Physics at the LHC, Sheffield May 08 15

Track Reconstruction efficiencies by track

insertion•Insert a track into a minimum bias event by overlapping an RDO-DIGI file of a single track event.

•Reconstruct merged event and look for inserted single track to determine efficiency.

•Uses InDetOverlay-00-00-02 (by Andrei Gaponenko)

D.Clements

Muons pT>0.5GeV

Muons pT>0.5GeV

Early Physics at the LHC, Sheffield May 08 16

PHOJET

PHOJET implemented in ATHENAImportant for systematic cross-checks

Early Physics at the LHC, Sheffield May 08 17

More work to be done

• Release 14• Multi-vertex analysis• Identification of SD, DD, ND?• Alignment study

Early Physics at the LHC, Sheffield May 08 18

Startup Conditions• Current expectations: 2 months single beam running from the end of

July– Beam stability poor

• Single beam running provides:– ‘Clean’ environment to study beam backgrounds: Beam halo and beam

gas– Alignment and commissioning of endcap systems

• When to switch-on?• Aim to trigger on beam gas and beam halo events

– Beam gas events distributed along Z following gas density– Beam halo events mainly coming from upstream tertiary collimators

(TCT)

n

Early Physics at the LHC, Sheffield May 08 19

L1 for single-beam running

• Make a trigger decision from a loose time coincidence between Beam Pickup (BPTX) and– 2 or more Minimum bias trigger scintillators (MBTS) above threshold

(MBTS overlaps EC-SCT)

OR

– 1 or more BCM above threshold

• The HV of the TGCs will be switched on when the beam is stable enough.

• The TGCs may be used to trigger on beam halo by faking a hit in the TGC1 station.– This is similar to the current cosmic setup in the barrel.

Early Physics at the LHC, Sheffield May 08 20

Track Reconstruction

• Beam halo tracks can be reconstructed by using cosmic style tracking code

• First go – beam-halo muons in endcap SCT

• Alignment• Rate ~130Hz?

A. Salzburger